Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Freon

Ammonia

Brine

Carbon dioxide

2. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Compressor and condenser

Receiver and evaporator

Condenser and receiver

3. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

4. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

1.25

2.15

5. The bank of tubes at the back of domestic refrigerator is

Refrigerant cooling tubes

Evaporator tubes

Condenser tubes

Capillary tubes

6. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

2.33

1.33

4.33

7. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

8. A bootstrap air cooling system has

Three heat exchangers

Two heat exchangers

One heat exchanger

Four heat exchangers

9. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

10. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Wet vapour

Saturated liquid

Superheated vapour

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11. Critical temperature is the temperature above which

A gas will immediately liquefy

Water will evaporate

A gas will never liquefy

Water will never evaporate

12. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

Negative

None of these

Zero

13. The freezing point of sulphur dioxide is

-77.7°C

-56.6°C

-135.8°C

-75.2°C

14. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Evaporator

Absorber

Condenser

15. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Any one of the above

Equal to unity

Always less than unity

16. The boiling point of ammonia is

-33.3°C

-10.5°C

-77.7°C

-30°C

17. For obtaining high COP, the pressure range of compressor should be

Optimum

High

Any value

Low

18. Freon group of refrigerants are

Nontoxic and non-inflammable

Non-inflammable and toxic

Toxic

Inflammable

19. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Ambient air temperature

Wet bulb temperature of air

Dew point temperature of air

20. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Relative humidity

Wet bulb temperature

Dew point temperature

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21. The domestic refrigerator uses following type of compressor

Axial

Centrifugal

Miniature sealed unit

Piston type reciprocating

22. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

None of these

Sub-cooling or under-cooling

Normal cooling

23. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

24. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

Low boiling point

Large latent heat

High risibility with oil

25. Rating of a domestic refrigerator is of the order of

10 tons

0.1 ton

40 tons

5 tons

26. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

9: 1

1: 1

1: 3

1: 9

27. The capillary tube, as an expansion device, is used in

Room air conditioners

All of these

Water coolers

Domestic refrigerators

28. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

None of the above

29. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Less

Unpredictable

30. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Reversed Carnot

Carnot

Rankine

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31. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Takes place at constant temperature

Involves no change in volume

Takes place at constant pressure

32. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

33. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

2 bar

30 bar

15 bar

34. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.376

0.67

0.6

35. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Above critical temperature

Near critical temperature of refrigerant

Much below critical temperature

36. Which of the following cycles uses air as the refrigerant?

Ericson

Bell Coleman

Stirling

Carnot

37. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

38. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

More for small capacity and less for high capacity

Less

39. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

40. Most thermostatic expansion valves are set for a superheat of

10°C

15°C

5°C

20°C

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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